1. Field of the Invention
The present invention pertains to biometric technology, and in particular, to fingerprint scanning.
2. Related Art
Biometrics is a science involving the analysis of biological characteristics. Biometric imaging captures a measurable characteristic of a human being for identity purposes. Fingerprint capture and recognition is an important biometric technology. Law enforcement, banking, voting, and other industries increasingly rely upon fingerprints as a biometric to store, recognize or verify identity. See, e.g., Gary Roethenbaugh, Biometrics Explained, International Computer Security Association, Inc., pp. 1-34, (1998), which is incorporated herein by reference in its entirety.
One type of biometric identification system that uses fingerprint imaging is an Automatic Fingerprint Identification System (AFIS). Automatic Fingerprint Identification Systems are used for law enforcement purposes. Law enforcement personnel collect fingerprint images from criminal suspects when they are arrested. In this case, a suspect's finger or fingers are imaged in a live scan. Law enforcement personnel also collect fingerprint images from crime scenes. These are known as latent prints. Ten-print scanners are a common type of AFIS system. Ten-print scanners produce forensic-quality ten-print records of rolled and plain impression fingerprint images.
In conventional fingerprint scanners, one or more fingers are placed in an imaging area. An illumination source illuminates the underside of finger(s). An image representative of valleys, ridges, and other minutiae of a fingerprint is then detected by an image sensor, such as, a solid-state camera. Fingerprint scanners use a surface of a platen as the imaging area.
In a live scan, one or more fingers are placed on the outer surface of the platen. Different types of fingerprint images often need to be detected depending upon a particular application. For example, a flat print consists of a fingerprint image of a digit (finger or thumb) pressed flat against the platen. A roll print consists of an image of a digit (finger or thumb) made while the digit (finger or thumb) is rolled from one side of the digit to another side of the digit over the surface of the platen. A slap print consists of an image of four flat fingers pressed flat against the platen.
In many fingerprint scanner systems, the platen is held in stationary position during a live scan. The optical imaging area which is detected at a given moment is the area where light from an illumination beam can reflect from the platen to the detector. A stationary platen generally needs to have a large optical imaging area to capture an adequate range of fingerprint images. As a result, a stationary platen requires a large imaging surface and a large area camera. This increases component cost and size. This is especially true for ten-print scanners such as those used with AFIS systems which need to capture individual flat prints, roll prints, and slap prints. Thus, a stationary platen is typically used in custom-made consoles that are expensive and large.
What is needed is a fingerprint scanner having a platen that moves relative to an optical imaging area of a detector. Because the movable platen can move, the optical imaging area and associated detector can be relatively small. Thus, a smaller platen and smaller camera, such as a linear sensor, can be used which reduces cost and size. See, e.g., the commonly-owned, co-pending U.S. patent application by W. Scott, entitled “Individualized Fingerprint Scanner,” Appl. No. 09/067,792 filed Apr. 28, 1999, incorporated herein in its entirety by reference.
A movable platen, however, can present problems during a live scan. In particular, during a live scan to take a roll print, a finger must generally roll at an accurate rate of rotation over an optical reading or imaging area. In this case, because of friction with the finger, the movable platen moves as the finger rolls. If the finger rotates too fast, then data is lost, requiring the procedure to be conducted again. Similarly, during a slap print, four fingers are placed on a platen and then moved in unison laterally across an optical reading or imaging area. If the fingers move too fast, then data is lost, requiring the procedure to be conducted again. In addition, rapid movement of a platen during a live scan (roll print or slap print) can lead to unnecessary wear or even damage at excessive speeds.